Conventionally, in lens barrels that include a lens supporting structure for holding the lens and moving the lens along the optical axis of the lens barrel, a lens frame holds the lens and is screwed into an adjusting ring that is mounted on the lens barrel, and a bayonet-type structure is used as the mounting structure of the adjusting ring to the lens barrel. For example, three projections formed at equal spacings around the outer periphery of the adjusting ring are aligned with three notches of three grooves formed around the inner periphery of the lens barrel. The three projections are passed through the notches, and the adjusting ring is rotated so the projections rotate in the grooves so that the projections are no longer aligned with the notches. Moreover, leaf springs are provided between the projections and the grooves so that the rotation of the adjusting ring presses the projections against the leaf springs that bend to exert a holding force between the adjusting ring and the lens barrel.
In such a conventional arrangement, adjustment along the optical axis is first achieved by rotating the lens frame in a screw connection with the annular adjusting ring that moves the lens frame back and forth along the optical axis to vary the spacing of the lens mounted in the lens frame and other lenses. Next, the lens is moved in a plane perpendicular to the optical axis by changing the fitting positions of the bayonet-type projections and grooves, for example, by rotating the adjusting ring by 120 degrees to align different projections and notches until the connection that optimizes the centering of the lens on the optical axis is achieved. When the optimum alignment is found, an adhesive is coated in the bayonet grooves at the optimum position to bond the adjusting ring to the lens barrel, thus completing the optical axis adjustment operation of the lens and the lens barrel.
According to the above method, it is necessary to rotate the lens around the optical axis in order to find the optimum position. When the lens frame is rotated relative to the annular adjusting ring in order to obtain the proper position of the lens along the optical axis, the force is transmitted to the annular adjusting ring and may cause it to rotate relative to the lens barrel. In this case, there has been the drawback that the leaf springs revolve together with the annular adjusting ring due to the frictional resistance with the annular adjusting ring. If the direction of rotation of the annular adjusting ring is in the same direction as the direction of releasing the annular adjusting ring from the lens barrel, the tight connection between the annular adjusting ring and the lens barrel intended to be provided by the leaf springs is loosened. This increases the time required to make the proper optical axis adjustments.
Moreover, the leaf springs are provided for the original optical axis adjustment, but they are not needed after the adjustment is fixed by adhesive. However, the leaf springs cannot be removed and thus they remain in the lens barrel even though they no longer serve a useful purpose.